It's no secret that a player's choice in loudspeaker plays a big role in their tone. What's not as well know is that several elements other than the speaker itself also contributes to its sound, such as the type of cabinet. This includes the size of the cabinet, type of wood, thickness of baffle (the panel that the speaker is mounted to) and how the parts of cabinet are joined together. But out of all the elements of a cabinet's construction, the most significant aspect is arguably whether the back is opened or closed; The same amplifier will sound significantly different when driving speakers in either open back or closed back cabinets.
Open Back Cabinet
Most open back cabinets are actually just partially open, with upper and lower panels covering half or more of the back. They allow some of the speaker sound to radiate from the back and to a lesser extent, the sides. In general, open back cabs have a room filling quality that sounds open and natural. Without a complete back panel that compresses the speaker's voice, open back cabinets might be considered a more organic representation of a guitar sound. High frequencies in particularly benefit from this as they have lots of presence. The low end will tend to feel looser.
On stage, the extra radiance of sound can be helpful when there are no monitors. In the studio it provides some excellent options in terms of microphone placement. A slightly different tone will be available at the back of the cab and the use of an isolation booth can help create a more complete soundscape than you could capture using multiple microphones.
Closed Back Cabinet
Unlike the open back cabinet, closed back cabs can really only project the sound forwards, meaning no back spill or side leakage from the cabinet. This tends to accentuate and harden midrange and bass sounds, giving them a greater amount of low end punch. This increased directionality can make them harder to hear on stage unless you're directly in front, but is a very helpful for sound-men who would otherwise have to deal with the ambient 'wash' produced by an open back cabinet.
The Right Choice
As a rule of thumb, closed back cabinets tend to project the sound forwards and yield a punchier, more structured tone with crisper definition while open back cabinets are much more likely to fill the room they are in, providing a more natural and organic sound with a greater ambient quality. Just like with all tone-based decisions, the right choice comes down to your own style and what type of sounds you're looking for. With all the above information in mind, you should take every opportunity to play as many different types of cab as possible, open back or closed back, as well as every kind of speaker you can find. Trust your ears and they'll help you find what you like the sound of most.
Your Turn to Sound Off!
Which type of cabinet do you prefer and why?